1. Field of the Invention
The present invention generally relates to a clock adjusting device for use with a data reproducing apparatus and for an optical disc device, a magneto-optical disc device and the data reproducing apparatus, and more particularly to the clock adjusting device for adjusting a phase of a clock used for the data reproducing apparatus that samples a reproduction signal from a recording medium synchronizing with a predetermined clock and restores record data based on a sample value.
Moreover, the present invention relates to an offset detecting device that can be used for such the clock adjusting device.
Furthermore, the present invention relates to the data reproducing apparatus in which such the offset detecting device is applied.
2. Description of the Related Art
In recent years, a recording medium, for example, a magneto-optical disc has been improved in high density of recording information, and improvement in a transmission rate of data in a reproduction system of the magneto-optical disc is also attempted. Thus, a record reproduction method of PRML (Partial Response Maximum Likelihood) is proposed as an approach of reproducing information at high speed and with high accuracy from the magneto-optical disc in which the information is recorded at high density.
In the record reproduction method of this PRML, data to be recorded is written on the magneto-optical disc by a signal of a partial response (PR) waveform. And the data is sampled a reproduction signal from the magneto-optical disc synchronizing with a predetermined clock and in accordance with a maximum-likelihood (ML) decode algorithm (for example, Viterbi decode algorithm), probable data is restored from a sample value.
In the data reproducing apparatus (for example, optical disc device) on condition of the above-mentioned record reproduction approach of PRML, the reproduction signal from a recording medium, for example, it is necessary to sample a magneto-optical disc synchronizing with the clock and to adjust the phase of the clock so that a sample value turns into a value by which a partial response waveform is characterized. For example, in a case of PR(1,1) waveform, the sample value becomes a peak value (2), a center value (1), or a bottom value (0).
The clock adjusting device known from the former converts a reproduction signal into two values by predetermined slice level and adjusts the phase of the clock so that the phase of the clock synchronizes with a rising edge (leading edge) or falling edge (trailing edge) of the two-value signal by a PLL (Phase-locked loop) circuit. By such a phase adjustment device, the phase of the clock is adjusted so as to synchronize with the rising edge or falling edge of the reproduction signal.
In the above-mentioned phase adjustment of clock signals, a phase error amount of the clock is calculated based on a relationship between a reproduction signal and a clock (for example, a relationship between the phase of the rising edge of the reproduction signal and the phase of the clock), and the phase of the clock is adjusted so that the phase error amount is eliminated. Accordingly, if there is a local skew in the reproduction signal or a level fluctuation (envelope fluctuation) in the over all reproduction signal, a stable phase adjustment cannot be realized.
It is a general object of the present invention to provide a clock adjusting device for use with a data reproducing apparatus and for optical disc devices, a magneto-optical disc device and the data reproducing apparatus in which the above-mentioned problems are eliminated.
A first specific object of the present invention is to provide the clock adjusting device that can perform stable phase adjustment.
A second specific object of the present invention is to provide an offset detecting device that can be used for such the clock adjusting device.
A third specific object of the present invention is to provide the data reproducing apparatus in which the offset detecting device is applied.
The above first object of the present invention is achieved by a clock adjusting device for use with a data reproducing apparatus for a reproduction signal from a recording medium is sampled synchronizing with a predetermined clock and data is restored in accordance with a maximum-likelihood decode algorithm corresponding to a record rule of a partial response using a sample value, the clock adjusting device including: a phase error detecting part detecting a phase error amount of a clock based on a state of the sample value at a first edge of the reproduction signal on a basis of a reference level; an offset detecting part detecting an offset amount of the reproduction signal; a reference level adjusting part adjusting the reference level used by the phase error amount detecting part based on the offset amount detected by the offset detecting part; and a phase adjusting part adjusting a phase of the clock based on the phase error amount detected by the phase error detecting part, wherein the offset detecting part includes: a monitor sample value generating part generating a monitor edge sample value based on the sample value at a second edge being an opposite side edge to the first edge of the reproduction signal; and an offset calculating part for calculating, as an offset amount, a change amount of the monitor edge sample value generated by the monitor sample value generating part based on the monitor edge sample value obtained at a predetermined timing.
In the clock adjusting device, since the reference level in the phase error detecting part is adjusted based on the offset amount even if it fluctuates the overall level of the reproduction signal, the more proper amount of phase errors can be obtained.
Moreover, the offset amount is calculated based on the change of the monitor edge sample value generated based on the sample value. Therefore, it is possible to obtain the offset amount by digital process.
The monitor edge sample value may be the sample value itself. Alternatively, the monitor edge sample value may be a rough level of a plurality of sample values. From a viewpoint that the offset value is not influenced by a rapid fluctuation of the sample value, it is desirable that the monitor edge sample value indicates a rough level of the plurality of sample values, such as an average value of those sample values.
Moreover, the above first object of the present invention is achieved by the clock adjusting device, wherein the first edge is a leading edge of the reproduction signal, and the second edge is a trailing edge of the reproduction signal.
From a viewpoint that a stable phase adjustment can be conducted form an earlier stage of a phase adjustment, in which stage the phase of the clock is greatly shifted, the above first object of the present invention is achieved by the clock adjusting device further including: a part detecting the phase error amount based on the change state of a plurality of sample values; and a phase error switching control part controlling the phase adjusting part so that the phase of the clock is adjusted based on the phase error amount obtained by the phase error detecting part after the phase of the clock is adjusted based on the phase error amount detected by the part.
The above second object of the present invention is achieved by an offset detecting device for detecting an offset of a reproduction signal in a data reproducing apparatus that the reproduction signal from a recording medium is sampled synchronizing with a predetermined clock and data is restored using a sample value in accordance with a maximum-likelihood decode algorithm corresponding to a record rule of a partial response, the offset detecting device including: a monitor sample value generating part for generating a monitor edge sample value based on the sample value at a second edge being an opposite side edge of a first edge of the reproduction signal when the reproduction signal is sampled synchronizing with the clock which phase is adjusted to the first edge of the reproduction signal; and an offset calculating part calculating, as an offset amount of a reproduction signal, a change amount of the monitor edge sample value generated by the sample value generating part on a basis of the monitor edge sample value obtained at a predetermined timing.
The above third object of the present invention is achieved by an apparatus for reproducing data, including: a first processing part sampling a reproduction signal synchronizing with a first clock which phase is adjusted to a first edge of said reproduction signal from a recording medium, and restoring data in accordance with a maximum-likelihood decode algorithm corresponding to a record rule of a partial response by using a first sample value; and a second processing part sampling said reproduction signal synchronizing with a second clock which phase is adjusted to a second edge being an opposite side edge of said first edge of said reproduction signal, and restoring data in accordance with said maximum-likelihood decode algorithm by using a second sample value, wherein said first processing part includes: a monitor sample value generating part generating a monitor edge sample value based on said second sample value at said second edge of said reproduction signal; an offset calculating part calculating, as an offset amount, a change amount of said monitor edge sample value generated by said sample value generating part based on said monitor edge sample value obtained at a predetermined timing; and a part supplying said offset amount obtained by said offset calculating part to said second processing part, so that said first processing part and said second processing part restore data based on said reproduction signal and said offset amount.